Wind and energy harvesting systems suffer from the problem of what to do when the winds are calm or wind speed varies significantly. The resulting variation of input from the wind energy source to the grid can cause trouble if the wind energy source makes up more than a few percent of the total capacity of the grid. Similarly, when the winds have high amplitude and the electric generators are running at maximum power, the excess power put into the grid can also cause troubles if it is not needed. Furthermore, there are times of peak demand when the price paid for electricity can be many times higher than off-peak, and thus it would be advantageous to be able to provide as much power as possible during peak demand.
It is well known that on land, excess wind power can be used to pump water uphill to a reservoir; however, this approach is often done with great environmental damage because the tops of mountains must be removed, or rivers dammed. Furthermore, water is pumped uphill into an open reservoir, and much is lost to evaporation.
Offshore, the emphasis has been on making the cheapest, most unimposing support structure possible for wind turbines. It has been assumed that when wind capacity is low, onshore generating stations will compensate for the fall in capacity. However, this is not the case when turbines are placed far offshore, where the wind is fairly regular. Far offshore, water depths greater than a hundred meters require wind turbines to be supported by floating structures which must be moored to the seabed. One existing example is the “Hywind” project in the North Sea which is operated by Norway's Statoil. Here, a wind turbine is mounted on a spar buoy moored to anchors and the generated power is transmitted along a cable attached to the mooring line. The cables run along the sea floor to a central station that can collect power from many systems and conditions it (e.g., turn it into high voltage DC so field lines do not couple with the salt water) to transmit it to land.
To ensure a reliable, demand-driven supply from these offshore turbines as wind speeds vary, an energy storage system with a capacity greater than 20% of the daily energy production capacity of the wind turbine (or 4 to 10 hours of storage) is needed. NREL has determined that storage can greatly improve increased penetration of renewable energy sources such as solar and wind, and storage is necessary if renewables are to be able to be used to satisfy baseload demand without acquiring additional combustion gas turbine reserves. Satisfying baseload demand is crucial to reducing CO2 emissions by replacing coal power plants with baseload renewable power. The energy storage system is also needed to smooth out power spikes from the wind turbine so that the HVDC line to land can be sized for average power production.
Numerous studies have shown the benefits of load-leveling, in which fossil-fueled plants run at a constant base-load and storage is used to handle peak loads and is re-charged during off-peak periods. This approach allows power plants to run at a more efficient setting, minimizes wear and tear on the machinery as it ramps up and down daily, and reduces wasted power due to transmission losses during peak demand periods. Large-scale energy storage, especially near the greatest load centers along the coasts, would increase the amount of level loading available and can actually reduce fuel usage and reduce emissions, even despite efficiency losses of the storage device.
Furthermore, another application for the invention pertains to during hurricane season in the Gulf of Mexico, numerous oil platforms and rigs must conduct “shut-in” procedures in order for personnel to evacuate. During “shut-in” times production ceases which results in lost present-value profits during that period. A means of collecting oil during hurricane “shut-in” periods would allow the well to continue production without risking personnel safety. During the large oil leak, commonly referred to as the “Deepwater Horizon” event at the Macondo Prospect in the Gulf of Mexico, oil was eventually able to be collected as procedures and equipment to cap the well were developed. However, a tropical storm required evacuation of the ships collecting the oil and oil continued to leak while personnel evacuated the area. A means of collecting oil in deepwater at the site during this evacuation period would have reduced the total amount of oil spilled.
An object of this invention, therefore, is to provide an offshore energy storage and electric power generation system structure that can moor offshore energy harvesting machines (e.g., wind turbines, water turbines, wave energy machines) and also provide energy storage capability.
A further object of the invention is to provide energy storage capacity with a large chamber deep below the surface of the ocean into which water can flow past hydro turbines to generate electricity when the amplitude of wind, currents, and/or waves is low in order still to generate electricity continually.
A further object of the invention is to provide energy storage capacity with a large chamber deep below the surface of the ocean from which water can be pumped using hydro turbines to generate energy storage capacity when the amplitude of wind, currents, and/or waves are such that they are generating excess electricity.
A still further object of the invention is to use a heavy ballasted structure to anchor the energy harvesting structure to the sea floor by virtue of its mass.
A still further object of the invention is to hold the structure in place on the sea floor by piles, grouting, or suction anchors.
A still further object of the invention is to use a central energy storage/generating chamber to serve the needs of multiple surrounding wind, ocean current and/or wave energy harvesting machines.
A still further object of the invention is to load-level on-shore power plants for increased overall efficiency, reduced emissions, and reduced fuel usage.
A still further object of the invention is to store hydrocarbons in the vicinity of undersea wells during hurricane shut-in procedures and during potential well leaks, allowing more rapid retrieval of the hydrocarbons once oil platform/rig operations are allowed to continue safely.
A still further object of invention would be to store energy hydraulically for powering offshore oil platforms and subsea equipment in the case of generator failure. Subsea equipment is presently powered by generators located on platforms that transmit power to the floor with large subsea umbilical cables. If there is an interruption of power on the surface (generator failure), this invention could provide backup power during this down time.
Other and further objects will be explained hereinafter and more particularly delineated in the appended claims.